The third generation of biodiesels, derived from microalgae, is one of the most interesting options for the replacement of fossil fuels. While the use of first generation biodiesels on different types of compression ignition engines is well documented in the open literature, much less information is available on algal fuels. As a matter of fact, the influence on combustion and pollutant emissions is not definitively assessed, depending on the combination of the specific features of both fuel and engine.The aim of this paper is to analyze the combustion process in a small industrial engine fueled by an algal Biodiesel, blended with standard Diesel fuel. The blend composition is the one typically used in most applications, i.e. 20% of biodiesel and 80% of Diesel (B20). In order to give a rigorous reference, all the experiments have been repeated with pure Diesel fuel, and with a blend made up of 20% of commercial rapeseed biodiesel, one of the most representative first generation biofuel.The experimental campaign has been carried out on an IDI 4-cylinder 1.4 liter naturally aspirated engine. It was found that the algal B20 slightly improves fuel conversion efficiency, in comparison to standard Diesel. This result is due to the different combustion rate, as well as to a more complete burning process. Differently from previous studies, no advantage has been found in terms of soot. Finally the algal B20 requires a higher fuel mass flow rate in order to compensate the lower heating value.